Gate valves having discs moved into position to close apertures have long been known. Thus, U.S. Pat. No. 786,043--Gustavus T. Luckett--Mar. 28, 1905, shows a typical gate valve in which two substantially flat back to back discs are arranged to be seated and unseated by means of a suitably actuated stem.
Another version of these valves, also known as a "loose-seat gate valve" is shown in U.S. Pat. No. 1,586,345--Wylie G. Wilson--May 25, 1926, where the two discs are pressed apart by a spring to establish and maintain a seal between the sealing element of the valve and its seat. Provision for convenient and expeditious repair is its objective.
Conventional valves of this type are subject to wear by the fluid flow through the valve resulting in a weardown of the edges of the control disc. This not only changes valve closure characteristics in the flow path, but also prevents the operation of the shear cleaning action of the disc in passing across the aperture facing, even to the extent of letting particles ride between the disc and seat. Thus, the life of these valves is materially shortened.
Thus, it is an objective of this invention to improve the long life characteristics of such gate valves and to correct the wear deficiencies of the prior art.
It is noted that the above cited U.S. Pat. No. 786,043 attempted to solve the problem of wear on the edges of the control disc by provision of a series of lugs on the discs which engaged with rigid studs on the side of the valve chamber, thus creating a ratcheting effect, thereby causing the valve discs to be revolved, always in the same direction, by means of the opening and closing of the valve.
This structure, however, has various shortcomings. Thus, for example, the discs must be turned by closure force from the stem as they are being seated in a position where they are being wedged tightly against the seats. This wears and tends to cause leakage through the packing ring, which of itself reduces the valve life.
It is a further objective of this invention to simplify the construction of this type of valve, and improve upon the solution to the wear problem.